A registered design is a legal right
A registered design is a legal right which protects the overall visual appearance of a product in the geographical area you register it. The visual features that form the design include such things as the lines, contours, colors, shape, texture, materials and the ornamentation of the product which, when applied to the product, give it a unique appearance. You can also register a design showing the ornamentation alone e.g. a pattern to go on a product or a stylized logo.
A registered design can be a valuable asset, allowing you to stop others from creating designs which are too similar to yours within the same geographical area you have protected your design - registration gives you protection for the visual appearance of the product but not for what it is made from or how it works. To be registrable, a design must have individual character and also must be new.